Soil3 - Sustainable subsoil management
Rising populations worldwide demand greater efforts to meet the resulting demand for food in a socially and environmentally compatible and sustainable manner. This is a major challenge, because in Germany and around the world, the amount of land available for arable farming is steadily decreasing and the risk of crop failures during warm and dry summers is increasing, while the availability of fertilizers is decreasing or the costs for them are rising.
So far the subsoil has hardly been considered in management strategies, although it stores large stocks of water and nutrients which might contribute to yield security and gain in productivity, especially in dry years or under conditions of nutrient deficiency. The aim of the Sustainable Subsoil Management (Soil3) project is to include the subsoil in management options. We hypothesize that water and nutrient uptake from the subsoil can be increased if attractive conditions are generated for the crop to invest in root growth in the subsoil. This can be accomplished through measures such as reducing physical resistance for the root, creating nutrient hotspots in the subsoil, or storing water in the subsoil when the topsoil dries out due to seasonal conditions.
> 50%
of water and nutrient stocks are located in the subsoil
10-80%
of the water and nutrient demand of crops is covered by subsoil ressources
71%
of German arable soil is affected by root-restricting layers
Within the joint project Soil3, the follwoing measures are used: a) n a combination of deep-rooting pre-cultures with mechanical techniques, the soil chemical, physical and biological properties of the subsoil are to be improved for plant growth. Here, the subsoil is heterogenized with a trencher and organic material is incorporated into the subsoil. In addition, b) an inventory and analysis of metadata from long-term field trials and data from the German Soil Inventory - Agriculture will provide information on nutrient conditions in the subsoil. This will enable us to test concretely, and also from the point of view of technical feasibility and socio-economic acceptance, how the total soil volume can be optimized for agricultural use.
Phase I (2015-2018): Proof of Concept
- Inventory and metadata analysis on subsoil ressources and their accessibility
- Improved subsoil accessibility through deep-rooting pre-cultures and mechanical subsoil melioration (development of prototype in central field trials)
Phase II (2018-2022): Proof of Feasibility
- Improved understanding of interactions between root penetration resistance, nutrient and water status and utilization of subsoil ressources
- Further development and application of tools for detection of effects of subsoil melioration on water and nutrient uptake
- Estimation of benefits and sustainability of subsoil melioration under contrasting site conditions
Phase III (2022-2025): Proof of Sustainability, Upscaling, Implementation
- Proof of sustainability of the Soil3 technique
- Upscaling of findings on national scale
- Implementation in consultation tool (Impact Assessment Platform)
The on-going data acquisition in the field trials in phase III records mit-term effects of subsoil melioration and is a follow-up of the studies that started in phases I and II. Besides delivery of field and agronomic data as well as soil quality data, the focus is still on subsoil accessibility.
All findings from the central field experiments and on-farm demo trials will be integrated into teaching materials and consultation measures for farmers and scientists (product category 3) as well as into the Impact Assessment Platform (product category 4).
In product category 2, three pillars for product category 3 are built: i) selection of compost material, ii) indicators for the sustainability of subsoil melioration and iii) mathematic tools for the prediction of success of the melioration measures.
The decision support tool for the compost selection is based on the stoichiometry of the compost mixtures and will be generated with the help of a microcosm experiment, in which on the one hand the interaction of soil type, compost type and soil moisture with regard to nitrogen dynamics and on the other hand the role of microorganisms in an efficient nitrogen cycling will be examined.
As indicators for sustainability, we use i) the ability of the Soil3 technique to enhance soil carbon stocks on the long-term or not to release these under changing climatic conditions, respectively, ii) the nutrient use efficiency in different soils and by different crops and iii) the estimation of the biological risk via arbuscular mycorrhiza and saprotrophic fungi.
Based on mathematic tools, nutrient use efficiencies and potential yield gains are modelled under different scenarios, and the longevity of the improved soil structure is calculated. Moreover, the plant growth model is used to quantify yields and further indicators for different climatic scenarios.
The implementation of the Soil3 technique requires that stakeholders such as farmers, policymakers or public authorities are well informed about background as well as technical and economical characteristics. Therefore, various information materials are generated in order to involve the public, industry, science but also schools. By means of movies in which the Soil3 technique and its benefits are explained, subsoil management and its usefullness are brought into the focus of the broader public. With a documentary film about subsoil management, scientific and non-scientific interested parties are addressed. A policy paper will give recommendations for actions within the political frame of subsoil management. The handbook will contain basic information on compost selection and procedure costs, and will be divided into the three main aspects i) decision fundamentals, ii) technical advice and iii) societal benefits.
An overall aim of phase III is to give region-specific decision support for the application of subsoil management in the agricultural practice. This will be accomplished with the Impact Assessment Platform. For its development, region-specific compsot data and parameters for the geographic suitability (soil type, climate) for subsoil management are required. For the compost selection, on the one hand results from product 3 on site suitability will be integrated, on the other hand also regional disposability of different compost materials will be investigated as an important factor for application of the Soil3 technique. For the suitability map, GIS data including e.g. stone contents will be regionalized with the help of algorithms, and elimination criteria are generated, so that finally a recommendation ("suitable", "likely suitable", "unsuitable") can be given. This map will further be linked with data on subsoil water use and on nitrogen leaching risk, and supported by a model to predict site-specific effects of subsoil management on yields and nutrient uptake. As a last point, cost-benefit analysis on mechanical and biological subsoil melioration will be integrated into the development of the Impact Assessment Platform, thereby also taking into account socio-economic factors. Finally, the Impact Assessment Platform will be optimized by testing and evaluation together with users in workshops.